[cairo] transforming text

[Matt Bartolome]

On Wed, Aug 5, 2009 at 11:08 AM, Behdad Esfahbod<behdad at behdad.org> wrote:
>
> On 08/05/2009 01:47 PM, Matt Bartolome wrote:
>>
>> Hi,
>> I'm drawing in geographic units so I applied a transform and translate
>> to draw correctly in pixel space. This works fine. When I draw the
>> text using the same transformation it appears vertically reflected
>> (this is what I would expect it to do). How would you go about drawing
>> the text so it doesn't appear flipped, but still in the correct x,y
>> position and rotation? Attached is a clip of the image I'm getting,
>> obviously the text is wrong and is what I'm trying to correct.
>
> Hi Matt,
>
> Use a font matrix that reflects it back to normal.  cairo_set_font_matrix()
> for example.  It normally is just a scale the size of the font size.
>

Thanks for your help behdad,

Hmm, I'm still lost with how to use set_font_matrix. When I set it (I
must be setting it wrong) the output image isn't changing.

# scale
ctx.scale(scale,scale)

# flip y
matrix = cairo.Matrix(1, 0, 0, -1, 0, 0)
ctx.transform(matrix)

# output from 0,0
ctx.translate(xmin, -ymax)

# draw 2d profile line components
ctx = horizontal_center(ctx, sticks)
ctx = stick_head(ctx, sticks)
ctx = surface_elevations(ctx, sticks)

# now draw text
# I would think this would be where I would flip the text somehow in
the current matrix so it draws in the same place but is reflected to
the normal position, but not sure how to do it.
ctx.set_font_matrix(cairo.Matrix(1, 0, 0, -1, 0, 0))

ctx.new_path()
ctx.select_font_face('DejaVu Sans ExtraLight')
ctx.set_font_size(2)
ctx.set_source_rgb(0, 0, 0)
ctx.move_to(x, y)
ctx.rotate(math.atan(slope))
ctx.show_text("test")
ctx.restore()

Thanks for your help!

> Cheers,
> behdad
>
>
>> Hints, pointers appreciated!
>> Thanks,
>> Matt
>>
>> #bounds in geographic units
>> xmin, ymin, xmax, ymax = max_bounds(sticks)
>>
>> #scale factor
>> scale_x = width / (xmax-xmin)
>> scale_y = height / (ymax-ymin)
>> scale = min([scale_x, scale_y])
>>
>> ctx.save()
>> ctx.scale(scale,scale)
>> #flip y
>> matrix = cairo.Matrix(1, 0, 0, -1, 0, 0)
>> ctx.transform(matrix)
>> #output from 0,0
>> ctx.translate(xmin, -ymax)
>>
>> #draw 2d profile components
>> ctx = horizontal_center(ctx, sticks)
>> ctx = stick_head(ctx, sticks)
>> ctx = surface_elevations(ctx, sticks)
>> ctx.restore()
>>
>> #at this point I would like to draw the text somehow with the proper
>> transform, rotation etc...
>> ctx = draw_text(ctx,sticks)
>>
>> surface.finish()
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>